Is the cast confirmed?

So it's not called Steves Umbrella anymore I assume?

He was great to work with on Once Upon A Time. He played The Mad Hatter. They went over his backstory to how he became trapped in Wonderland, by The Evil Queen "Regina" (Snow White's step-mother, just to clarify) whom he was friends with before he stopped traveling via a magical hat after the death of his wife/mother of his daughter. Regina convinced him to go on "one more trip to get something that was taken from [her]." Apparently the hat would allow only the same number of people who went into the hat (and access to all of the various realms within) to go back out through the hat - the caveat being they didn't have to be the SAME people.

The "something" stolen from Regina was her Father, by the Queen of Hearts, who was actually Regina's mother, Cora -Latin for HEART (btw). Cora was banished, unknowingly at the moment, by the yet to be Evil, Princess Regina (who was being forced by her mother to marry Snow White's, 3x her age, widower father) via a wedding gift from Rumplestiltskin of a magical mirror/portal (symbolism).

Now, years later, and Regina being the Evil Queen, she made the request of her old friend (Sabastion Stan's character), and Royal subject. He basically couldn't say no. He left his daughter for what thought was just going to be a few hours, with friends in a neighboring cottage, and agreed to help his old friend (remembering that they were friends long ago, and he felt guilty in the role he played in an important event in the innocent young Princess's life, with the help of Rumplestiltskin and Dr. Frankenstein, in having her lose all hope of love, thus becoming the Evil woman
she now was).

They went, just the two of them through the hat into Wonderland to stealthy get back her "possession" from her even more evil mother, Queen of Hearts. It turns out that it WASN'T a THING, but a WHO - Regina's loyal, exceptional kind, loving and devoted Father - King Henry. Cora had shrunk him, via the wonderful flora and fungi in Wonderland, to fit into a box that was identical to those in which she kept the hearts that she took from anyone who looked at her wrong (picture shoebox size). As they ran from the center of the hedge-maze, where the Queen of Hearts kept all of her thousands of stolen hearts, to the portal that was open via the hat - that The Hatter (still not "MAD") finally was shown the contents of the box, when Regina's father took a bite of a toadstool that reversed the original toadstools shrinking power. Now they had a major problem - THREE people couldn't leave when only TWO entered. Regina used her magic and had the hedge-maze hold Sebastian Stan while she and her beloved Daddy walked through to their realm in the Enchanted Forest.

Being stuck, and needing to get back to his daughter, The Hatter made hundreds in not thousands of hats, trying to find one that would have the same magical effects as the original that he created - and trapped him in Wonderland. He eventually went insane, and became The Mad Hatter.

Decades later, by following one of the White Rabbit's holes, he made his way to Storybrook (the land in modern-day Maine, USA that all the "characters" where sent to, after Regina enacted a curse to have all of the subjects in the Enchanted Forest lose their memories which were supplanted by new memories thanks to The Curse, Regina and Rumplestiltskin.) to enact revenge and find his daughter.

Sebastian Stan, was only in a few episodes, due to filming the second Captain America movie, "The Winter Soldier." Those few episodes showed so much range of the actor. Sorry to write such s long post, but I wasn't sure if anyone was familiar with the show (Once Upon A Time) and his amazing character arc in it. My cousin plays the character of Princess Regina/The Evil Queen/Mayor Regina Mills of Storybrook (Lana Parrilla). All of the cast were sorry to have Stan leave, and Jennifer Morrison (who plays the daughter of Snow White and Prince Charming) actually started a romantic relationship after meeting during filming on Once. I not sure if they are still together, but I know that they were in a long distance relationship during his filming and premiere of Caprain America: Winter Soldier.

Long story short, I have seen his rage before, and I know that he will be a great asset to this movie.